Using a previously validated and documented CFD methodology, this research simulated the flow field in the intake region (inlet duct, plenum, ports, valves, and cylinder) involving the four cylinders (#1, #3, #4, #6) of a straight-six IC engine. Each cylinder was studied with its intake valves set at high, medium and low valve lifts. All twelve viscous 3-D turbulent flow simulation models had high density, high quality computational grids and complete domains. Extremely fine grid density were applied for every simulation up to 1,000,000 finite volume cells. Results for all the cases presented here were declared “fully converged” and “grid independent”. The relative magnitude of total pressure losses in the entire intake region and loss mechanisms were documented here. It was found that the total pressure losses were caused by a number of flow mechanisms. The most important loss mechanisms included skin friction, separation, recirculation, reattachment, impingement, jet-to-jet interaction, high turbulence, and swirl and tumble type secondary flows. It was predicted that overall total pressure loss in the entire intake region decreased with increasing valve lift, and losses within the valve clearance region decreased with increasing valve lift. The comparisons of total pressure losses and flow fields were made between different simulations. An outstanding feature of the current study was the inclusion of physical mechanisms for valve lift variation of a single cylinder, and cylinder-to-cylinder variation of flows between different cylinders. From the comparisons, it was demonstrated that the results for all twelve cases had high internal consistency. By validation, the computed results obtained here showed consistent accuracy among all cylinders. Such consistency was obtained through careful application of the comprehensive methodology applied in this study.